In viscous clutches, the torque of a rotation source is transmitted via discs enclosing a shear region, a small distance apart and substantially parallel to one another, from the rotation source to an element to be driven. The amount of shear fluid which is introduced between the rotating discs into the shear region controls the degree of torque transmission between a lower threshold value, for example 10%, to virtually completely.
The control of the amount of shear fluid, for example silicone oil, which is introduced into the shear region is effected by a valve which can be opened and closed by means of an actuator. European Patent Application 1 248 007 describes such an actuator, which is arranged outside the clutch shaft and around the latter. Since the actuator is stationary and the clutch shaft rotates, it is necessary to use a correspondingly dimensioned ball bearing whose internal diameter according to the EP Patent Application corresponds to the external diameter of the shaft. For each shaft size, it is therefore necessary to use and especially to stock an appropriate ball bearing. Furthermore, the solution according to the EP Patent Application requires the use of insulating material.
It is an object of the present invention to provide an improved viscous clutch. It is also an object of the present invention to provide a viscous clutch which is smaller in size and is less complex than known viscous clutches.
It is an additional object of the present invention to provide a viscous clutch with an actuator which minimizes or eliminates the use of insulating material.
It is a still further object of the present invention to provide an actuator for the shear fluid circulation, for example of a viscous clutch, in which the size of the actuator components are substantially reduced which in turn reduces the size of the entire viscous clutch.